How to Choose and Use Graduated Filters
Graduated color and neutral density filters are valuable tools that help the landscape photographer balance brightness differences between foreground and background. Here are a few of my thoughts about them:
First, I only use the graduated neutral density filters. Other photographers use colored graduated filters for a variety of effects. Probably the commonest use of colored grads is to simulate sunset colors where they don't exist. Personally, that doesn't suit my taste or photographic style, so I don't use them. You might want to experiment with a "sunset" or a "tobacco" graduated filter and form your own opinion.
There are two dangerous pitfalls with ND grad filters. First, if the photographer overcompensates, the upper part of the photo will look artificially dark. For example, in the natural world, the reflection of a sky from a body of water is always darker than the sky itself. If a mountain's reflection off a foreground lake is lighter than image of the mountain itself, the picture will have an artificial appearance.
The second pitfall is the inclusion of foreground objects that cross into the background, such as a tall tree rooted in the foreground that climbs into a sky that needs to be darkened. If the bottom of the tree is normally exposed and the upper part of the tree is darkened and loses detail, the photo looks clumsy to me.
Plastic (aka "optical resin") filters last me about one use in the field before I scratch them. Others would argue that a few light scratches on a filter won't noticeably degrade the image. That may or may not be true, but a scratched filter will cause flare if sunlight falls directly on it, so why take a chance. With short focal length lenses on APS-C DSLRs like, for example, my Canon EF-S 10-22mm at 10mm stopped down to f/16, I feel I need to be careful about what is on my filter just a half inch from the lens. Besides, anytime I use equipment in which I don't have full confidence, it has an adverse impact on my work.
I use laminated glass graduated neutral density filters made by Tiffen. They are more expensive than plastic, but far more durable. The actual filter is a thin piece of plastic laminated between two pieces of clear glass. Tiffen claims that this construction yields more consistent and accurate results than dyed glass or plastic. All the major filter manufacturers make their screw-in polarizers using this technique.
I protect my filters from breakage by carrying them in a fitted padded case provided by Tiffen. I carry all 3 filters stacked together. It's harder to break 3 layers of laminated glass together than it is to break 1 packed by itself. Inside the padded case, I keep each filter in its own separate envelope. Each filter has a tiny sandblasted label on it, but for clarity and quick use in the field, I've numbered them with a large, easy to read label.
It can be tricky to position a grad in the right place to achieve a well-balanced result. Most of us have a tendency to overcompensate. What works well for me is to start with the grad high in the field of view, well above where I think it should be. Then I slide it down until its presence becomes apparent to my eye. It is now positioned too low. The effect that I see with the naked eye will appear greatly exaggerated in the finished photo. Next, I slowly slide the filter up until the bottom edge of the tinted area disappears and the luminence values blend together smoothly. I expose the shot, and then I check the histogram and also replay the image on the LCD display to make sure I got the shot.
ND grads are available in ND .3 (1 stop gradation), ND .6 (2 stops), ND .9 (3 stops) and ND 1.2 (4 stops). I think the most useful choices are ND .6 and ND .9. Most manufacturers now offer "hard edge" (a quick transition from clear to filtered) and "soft edge" (a gradual transition). I carry one square hard edge filter, a .6, and two long soft edge filters, a .6 and a .9.
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